The present invention relates to a thermal treatment apparatus used for a thermal treatment of a starting material, an intermediate product or a final product.
Various thermal treatment processes such as a heating process and a cooling process are employed in the processes of manufacturing various products such as a plasma display panel, a solar battery panel, a resistor chip and other devices and electronic parts. Numerous effects achieved by a thermal treatment are known. Specifically, drying, dehydration, calcination, reaction acceleration, surface modification, sealing, degassing, annealing and so on are known.
In a case where a heating furnace is used as a thermal treatment apparatus, the thermal treatment apparatus generally has a plurality of thermal treatment chambers arranged in the direction of transporting an object to be treated. Each thermal treatment chamber has a space provided therein in which the object is subjected to a thermal treatment, namely a thermal treatment zone. A heating furnace generally has a temperature raising zone (temperature raising chamber) in which the object is heated to rise in temperature, a thermostatic zone (thermostatic chamber) in which the object is maintained at the raised temperature, and a temperature lowering zone (temperature lowering chamber) in which the object is cooled down to decrease in temperature, as the thermal treatment zones. The object to be treated is subjected to predetermined thermal treatment processes while passing through each zone in the order described above. Typically, heat is applied in the temperature raising zone, while such an amount of heat is supplied which compensates for heat dissipation in the thermostatic zone, and heat is removed in the temperature lowering zone.
Therefore, the temperature raising zone and the thermostatic zone in which heat is applied to the object to be treated may also be called a heating zone. And the temperature lowering zone in which heat is removed from the object may also be called a cooling zone. The temperature lowering zone may also be called a slow cooling zone or a quenching zone depending on the decrease in temperature of the object which decrease is effected during the period from the entry of the object into the zone to the exit of the object from the zone (temperature decreasing rate). The slow cooling zone is generally a zone in which the temperature of the object entering the zone is lowered at a rate, for example, from several degrees to several tens of degrees Celsius per minute. The quenching zone is generally a zone in which the temperature of the object entering the zone is lowered at a rate of several hundreds of degrees Celsius per minute or higher.
Dimensions of the heating zone and the cooling zone are determined according to thermal treatment conditions on the basis of a throughput of the object to be treated, such as the time required for heating, cooling rate and a temperature of the object at the exit and the floor space required to install the thermal treatment apparatus.
In the case of a thermal treatment apparatus having a plurality of thermal treatment chambers, it is necessary to maintain the temperature in the thermal treatment chamber (namely the temperature in the thermal treatment zone) at a predetermined level so as to ensure that the predetermined thermal treatment effect is achieved in each of the thermal treatment chambers. For this purpose, temperature in the thermal treatment chamber is controlled by means of proper heating or cooling means and a temperature monitor.
The thermal treatment apparatus having a plurality of thermal treatment chambers may be a thermal treatment apparatus wherein an object to be treated is transported intermittently through the thermal treatment zones of the thermal treatment chambers, or a thermal treatment apparatus wherein an object to be treated is transported continuously through the thermal treatment zones of the thermal treatment chambers. An example of the thermal treatment apparatus wherein the object is transported intermittently is disclosed, for example, in Japanese Kokai Patent Publication No. 11-142061.
In the thermal treatment apparatus described in this publication, thermal separation between the thermal treatment zones is ensured by shielding each thermal treatment zone from other thermal treatment zones so that the thermal treatment zone will not be thermally influenced by the adjacent thermal treatment zones. Specifically, this thermal treatment apparatus has a shutter apparatus comprising a plate-like shutter disposed between heating zones and a pair of thermal insulating walls disposed to sandwich the shutter. The shutter is positioned at a shielding position where the heating zones are shielded from each other or at a retracted position where interference with the object being transported is prevented. That is, the shutter is placed at the retracted position when the object is moved between heating zones, and is placed at the shielding position when the object is moved into the heating zone. The object introduced into the heating zone is caused to stand still in the heating zone or to move back and forth therein so as to be subjected to a thermal treatment into a predetermined temperature.
In this thermal treatment apparatus, the shutter shields the heating zones from each other, while a thermal insulation effect is provided by the thermal insulating walls disposed at the border between the heating zones and an air layer formed between the thermal insulating walls. Thereby, each heating zone is thermally influenced as little as possible by the other adjacent heating zones. The air layer formed between the thermal insulating walls also prevents heat from being directly transmitted from the high temperature heating zone to the low temperature heating zone. Accordingly, in accordance with this thermal treatment apparatus, a temperature in each heating zone can be quickly controlled to the predetermined level after transporting the object intermittently and closing the shutter. In other words, this thermal treatment apparatus ensures independence of each thermal treatment zone by means of the movable shutter and the thermal insulating walls. This provides such advantages as the quality of the object can be assured and the total length of the thermal treatment apparatus can be made smaller.
Now the thermal treatment apparatus wherein the object to be treated is transported continuously is described below.
As an example of thermal treatment apparatus having a plurality of thermal treatment chambers wherein the object is transported continuously, there is one that applies a thermal treatment indirectly to the object while transporting the object in the thermal treatment chamber, called a muffle, which has a tunnel structure and is heated or cooled by proper heating or cooling means. The object is transported by conveyance means such as a mesh belt conveyor or a roller hearth. This type of thermal treatment apparatus is often called a muffle furnace or a muffle structure heating furnace. In the muffle furnace, the thermal treatment zone is defined by the muffle wall, and the thermal treatment zone is a thermal treatment atmosphere that is maintained at a predetermined temperature by heating means or the like installed outside the muffle.
The xe2x80x9cthermal treatment atmospherexe2x80x9d refers to a space in which an object to be treated is placed. Heat is applied to or removed from the object placed in this space by means of a gas contained in the space, a heating device, cooling device and/or the wall that defines the space. The xe2x80x9cthermal treatment atmospherexe2x80x9d is also referred to merely as an xe2x80x9catmospherexe2x80x9d. The gas included in the thermal treatment atmosphere is called an xe2x80x9catmosphere gasxe2x80x9d.
In the muffle furnace, the object is carried into the thermal treatment atmosphere and is desirably heat-treated by being heated or cooled indirectly via the inside surface of the muffle wall. Since the muffle furnace does not have heating means or the like in the thermal treatment zone, uneven heating in the thermal treatment zone and variations in the heating control due to the heater configuration can be mitigated. That is, since the thermal treatment zone has a more uniform thermal treatment atmosphere in the muffle furnace, it possible to apply a stable thermal treatment to the object to be treated with a desired temperature profile.
The muffle is typically a cylindrical structure made of a metal. The muffle is constructed, for example, in an integral cylindrical structure. Alternatively, the muffle may also be made in a square tube by forming the wall from thermal insulating blocks.
An example of the basic constitution of the muffle furnace is shown in FIG. 13. The muffle furnace (100) has a heating zone (heating chamber) in which the object to be treated is heated to rise in temperature and a cooling zone (cooling chamber) in which the object to be treated is cooled down to decrease in temperature arranged in the direction of transporting the object. The object undergoes predetermined thermal treatment processes while passing through the zones successively.
The muffle furnace shown in FIG. 13 is described below in more detail. A heating muffle (2) that forms the heating zone is made of a metal with the external wall thereof being surrounded by electric heater modules (1). The heating muffle (2) is heated by the electric heater modules (1) and is maintained at a predetermined temperature according to the desired thermal treatment. A cooling muffle (8) that forms the cooling zone is also made of a metallic material. A cooling water pipe (7) is provided on the external wall surface of the cooling muffle (8), so that the inside of the cooling muffle (8) is maintained at a predetermined temperature by the cooling water flowing in the cooling water pipe (7). The entire muffle including the heater modules (1) is surrounded by a wall (or an external panel) (110).
In the heating muffle (2), a mesh belt (3) that is a carrier moves continuously in one direction. An object (4) to be heat-treated is placed on the mesh belt (3) and moves from a loading section (5) to an unloading section (6). In the embodiment shown in the drawing, the mesh belt is disposed in parallel to the floor surface whereon the apparatus is installed (the X-Y plane in FIG. 13) and moves in the X direction.
As an alternative to the mesh belt, there is a carrier formed by arranging a multitude of cylindrical rollers with the longitudinal direction thereof disposed at right angles to the transporting direction and in parallel to the floor surface whereon the apparatus is installed (the X-Y plane in FIG. 13), namely in the Y direction in FIG. 13. Such a carrier is generally called a xe2x80x9croller hearthxe2x80x9d. When the roller hearth is employed, the object to be treated is transported by the rotation of the rollers.
The object to be treated (4) is heated while passing through the inside of the heating muffle (2) that is maintained at the predetermined temperature. After passing through the heating muffle (2), the mesh belt (3) and the object (4) pass through the inside of the cooling muffle (8). When passing through the cooling muffle (8), the object (4) is cooled down indirectly by the cooling water that passes through the cooling water pipe (7).
Now a section where two muffles are connected, namely the section around a joint of muffles is described below. FIG. 14 is a sectional view schematically showing the joint between the heating muffle (10) and the cooling muffle (13). The heater (9) is disposed around the heating muffle (10), and the cooling water pipe (11) is bonded onto the surface of the cooling muffle (13) by means of a heat resistant cement (12) or the like. The heating muffle (10) and the cooling muffle (13) are mechanically connected to each other by means of bolts/nuts (18) at joint members (a pair of flanges in the embodiment shown in the drawing) (16). A sealing member (17) made of a nonflammable material (for example, asbestos or nonflammable carbon material) is interposed between the joint members (16). The sealing member is used for preventing the atmosphere gas contained in the thermal treatment zones (14a, 14b) of the muffles (10, 13) from leaking through the joint to the outside atmosphere (15) of the muffles (10, 13). In such muffle furnace, the heating zones are hardly independent from each other since the object to be treated (25) is conveyed continuously.
In the muffle furnace described above, there is such a problem that only a very small part of the thermal energy supplied by the heater (9) is utilized for heating the object to be treated, namely an effective heat efficiency is very low. The term xe2x80x9ceffective heat efficiencyxe2x80x9d means the proportion of the thermal energy which is utilized for heating of the object to be treated to the thermal energy supplied to the thermal treatment apparatus by the heater (9). In a thermal treatment apparatus having a low effective heat efficiency, most of the thermal energy supplied by the heater (9) is waste energy that is not utilized in the thermal treatment, and may be called a heat loss.
For example, in a case where the object to be treated is a product such as an electronic component or electronic device, the effective heat efficiency when heating this object is 5% or lower despite the heat capacity of the object that is generally very small. This is because the thermal treatment is applied in a uniform, stable and large thermal treatment atmosphere for the purpose of maintaining satisfactory quality and yield of the product.
The lower the effective heat efficiency, the larger the amount of thermal energy that must be supplied to the thermal treatment apparatus. This results in a higher running cost of the thermal treatment apparatus and leads to an increase in the product cost. Thus, it is desired to reduce the cost by reducing the energy supplied to the thermal treatment apparatus (namely saving the energy). Particularly, it is strongly desired to develop an energy saving design for production facilities such as the thermal treatment apparatus that consumes a large amount of thermal energy, from the viewpoint of the effect of the production activities of corporations upon the global environment.
The effective heat efficiency tends to be lower in a thermal treatment apparatus having two adjacent thermal treatment chambers wherein a larger difference in the inside temperatures between the chambers is observed. That is, in the case of the thermal treatment apparatus shown in FIG. 13, the most heat loss occurs in the joint that connects the heating muffle (10) and the cooling muffle (13). The cause of heat loss occurring when heating an object to be treated in the thermal treatment apparatus that is a muffle furnace having a heating muffle and a cooling muffle as shown in FIG. 13 is described below, along with paths of heat transfer which the heat supplied to the heating muffle follows.
Part of the heat supplied from the heating means disposed around the muffle is transmitted through a heat transfer path including the furnace wall that surrounds the muffle. The heat transmitted through the path is released from the external surface of the furnace wall to the outside. The released heat does not reach the object to be treated, and therefore entirely amounts to heat loss.
Another heat transfer path is the water that flows through the cooling water pipe disposed outside the cooling muffle. Heat released to the outside from the water flowing through the cooling water pipe includes the heat radiated from the object heated in the heating muffle and the heat radiated from the carrier heated in the heating muffle. Specifically, the heat radiated from the carrier is eventually transmitted to the atmosphere gas in the cooling muffle and to the wall of the cooling muffle, or transmitted through contact of the carrier and the cooling muffle or thermal radiation occurring between the carrier and the cooling muffle wall to the wall of the cooling muffle. From the wall of cooling muffle, the heat is transmitted to the water that flows through the cooling water pipe disposed outside the cooling muffle so as to heat the water, and then, is released to the outside of the furnace.
Another path of heat transfer is the atmosphere gas. Release of heat through this path means that the heat is carried to the outside of the furnace by the supply and exhaust of the atmosphere gas. All the heat released in this manner amounts to heat loss. The amount of heat carried outside by the atmosphere gas varies depending on the method of applying the thermal treatment. When the thermal treatment is applied, for example, as a drying process for evaporating an organic solvent or the like, a larger amount of atmosphere gas is supplied and exhausted and the amount of heat removed also increases accordingly. When the quantity of solvent evaporated during the thermal treatment is small (for example, when a ceramic material is calcinated), on the other hand, a smaller quantity of the atmosphere gas is required to be supplied and exhausted. Therefore, the amount of heat carried to the outside of the furnace is much smaller than that released through the furnace wall and the cooling water.
Of the input thermal energy (100%) supplied to the thermal treatment apparatus such as the muffle furnace, a proportion of the thermal energy released through each of heat transfer paths described above varies depending on the type and operating conditions of the thermal treatment apparatus (such as a temperature, quantities of an atmosphere gas charged in and discharge from the thermal treatment zones, a transporting speed of the object to be treated and type of the object). In the case of a muffle structure heating furnace commonly used in electronic component manufacturing plants, for example, thermal energy released through the wall surface of the furnace is around 20 to 30% of the input thermal energy, while thermal energy released to the outside of the furnace by the cooling water is around 70 to 80% of the input thermal energy. Heat carried to the outside by the atmosphere gas is in a range from several percents to several tens of percents of the input thermal energy, depending on the discharging conditions of the atmosphere gas. The proportion of the thermal energy released through each heat transfer path can be calculated from the input energy, the temperatures in the thermal treatment chambers, temperature of the object to be treated, temperature and flow rate of the water flowing in the cooling water pipe and other data.
The reason for the greater proportion of the heat carried by the cooling water to the outside of the furnace may be due to the large amount of heat released from the carrier. The carrier is usually heated to the same temperature as the atmosphere gas in order to maintain the constant temperature around the object to be treated in the heating zone. The carrier is generally designed into such a construction that has a high strength at a high temperature so as to be capable of carrying the object in the thermal treatment space. As a result, the carrier tends to be large in size, and the heat capacity of the carrier inevitably becomes large accordingly. The larger the heat capacity, the larger the energy required to raise the temperature. Consequently, when the carrier is cooled down, a large amount of heat stored in the carrier is released. The carrier is indispensable for transporting the object to be treated into the atmosphere of the desired temperature in the thermal treatment apparatus. However, since the thermal energy released from the carrier has been supplied thereto merely for the purpose of maintaining the constant temperature around the object in the heating zone, it constitutes the heat loss. This heat loss typically accounts for around 20 to 30% of the input thermal energy.
The cause and amount of heat loss have been elucidated to some extent as described above, although not fully investigated. For example, on the assumption that the heat transmitted to the object is released in the cooling zone, when the heat released from the object to be treated and the heat released from the carrier are deducted from the heat carried by the cooling water to the outside of the furnace, the rest of the heat is about 30 to 50% of the input energy. However, the rest of the heat has not been closely studied with regard to the transfer path thereof.
The present invention has been made in consideration of the circumstances described above, and an object thereof is to provide a thermal treatment apparatus having an improved effective heat efficiency by elucidating the structural problem of the thermal treatment apparatus by finding out the causes of the heat loss and determining the contribution of each cause to the heat loss.
The present inventors have intensively studied about the heat loss. Through the study, it has been found that, of the heat released from the water that flows through the cooling water pipe in the muffle furnace described above, heat corresponding to about 25 to 45% of the input thermal energy is caused by the thermal conduction from the muffle wall that defines the heating zone to the muffle wall that defines the cooling zone. The present inventors have completed the thermal treatment apparatus of the present invention that involves a smaller heat loss than that of the prior art by providing the thermal treatment apparatus with means for effectively suppressing the thermal conduction.
The present inventors have also found that heat corresponding to about 5 to 20% of the input thermal energy is caused by the convection between the atmosphere in the heating muffle and the atmosphere in the cooling muffle, and radiation heat transfer from the inside surface of the heating muffle wall to the cooling zone. Accordingly, the present inventors have completed the thermal treatment apparatus of the present invention in which the heat loss is still smaller, by providing means for effectively suppressing the heat transmission through convection and radiation along with the means for suppressing the thermal conduction between the muffles.
FIG. 12 shows an example of a heat balance diagram in an electrically heated muffle furnace of the prior art, which diagram the present inventors have built according to the newly obtained finding. FIG. 12 is a heat balance diagram with respect to a thermal treatment wherein an object is calcinated and no evaporation is accompanied and accordingly only a small quantity of atmosphere gas is charged and discharged. The heat balance diagram shown is merely an example, and the proportion of released beat varies depending on such factors as the type of thermal treatment and operating conditions of the furnace.
As used herein, the term xe2x80x9cthermal treatmentxe2x80x9d refers to a treatment of heating the object to be treated, maintaining or decreasing a temperature of the object, or any combination thereof. Thus, it should be noted that the thermal treatment may be raising or lowering the temperature of the object, maintaining the object at a constant temperature or a combination of any of these, and therefore the thermal treatment may be a supply of heat to the object to be treated, removal of heat therefrom or any combination of these (including optional thermal insulation of the object). Through the thermal treatment, predetermined change is caused in at least one of properties of the object to be treated (such as a moisture content, a weight, an electrical resistivity, a permeability, a thickness of a resulted film or its uniformity, an internal stress or strain, a strength, a composition or the like).
The treatment in which heat is supplied to the object to be treated (i.e. heating treatment) includes, for example, a treatment of raising the temperature of the object to a predetermined level in a predetermined period of time, a treatment of maintaining the object at the predetermined temperature for a predetermined period and a treatment of subjecting the object to temperature change in a predetermined manor. The treatment in which heat is removed from the object to be treated (i.e. cooling treatment) includes a treatment in which heat is not supplied, namely a spontaneous cooling treatment, and a forced cooling treatment for lowering the temperature of the object by blowing cool air using power or not by means of a heat absorbing or heat radiating surface that can be controlled to a predetermined temperature. Also the cooling treatment includes the slow cooling described previously. In a case where the object to be treated is cooled gradually, the object may be subjected to a cooling treatment in a thermal treatment zone that is heated by a heater or other means to a temperature lower than that of the object in order to avoid quick temperature decrease. It should be noted that a thermal treatment carried out in the thermal treatment zone that is heated is also regarded as the cooling treatment as long as the temperature of the object is decreased.
Now the thermal treatment apparatus of the present invention, namely the thermal treatment apparatus provided with means for effectively suppressing the thermal conduction between the muffle walls is described below.
The thermal treatment apparatus according to a first aspect of the present invention comprises a plurality of muffles as thermal treatment chambers so as to apply a thermal treatment to an object to be treated that is being transported through the muffles, wherein at least one pair of two adjacent muffles of which inside temperatures are different from each other are connected through a thermal insulating structural member and the thermal insulating structural member has a tunnel structure so as to allow the object to pass therethrough.
The inside temperature of the muffle is in general the temperature of the atmosphere gas contained in the muffle. Thermal conduction occurs between two muffles of which inside temperatures are different. The thermal treatment apparatus of the present invention reduces heat loss caused by the thermal conduction between muffles by interposing the thermal insulating structural member between the two muffles where such thermal conduction occurs.
The thermal insulating structural member refers to a member that is formed so as to reduce the thermal conduction between the muffles. The thermal insulating structural member has a tunnel structure so that transportation of the object to be treated between the muffles is not impeded, and the object can pass through the thermal insulating structural member.
The fact that the thermal insulating structural member has a tunnel structure means that the member has a hollow which is open at an inlet and an outlet thereof so that the object to be treated introduced through the inlet is carried outside from the outlet. That is, the thermal insulating structural member of tunnel structure has a space that is present through the thermal insulating structural member along the direction of transporting the object. Any cross section obtained by cutting the hollow at right angles to the object transporting direction does not form a completely closed plane and always has an open portion. Therefore, in a case where the thermal insulating structural member is disposed between the adjacent muffles that serve as thermal treatment chambers, the tunnel structure of the thermal insulating structural member provides a passage that communicates between the thermal treatment chambers. Such a tunnel structure can be formed by defining the hollow with a wall.
The thermal insulating structural member used in the present invention also has a substantial length (dimension) in the direction of transporting the object to be treated. In other words, the thermal insulating structural member is not a plate or sheet configuration.
The thermal insulating structural member that is provided to reduce the thermal conduction between the muffles is constructed specifically as follows.
(1) A wall of the thermal insulating structural member is made of a material that has a lower thermal conductivity than that of the material which constitutes the muffle. By using the material that has a lower thermal conductivity, thermal conduction from a heating muffle to a cooling muffle can be effectively suppressed.
(2) The thermal insulating structural member is constructed in such a configuration in which a wall thereof has a non-uniform wall thickness, namely the wall has a smaller thickness in part. When the wall has a smaller thickness in part so as to decrease the area of cross section that is perpendicular to the direction of thermal conduction, for example, the direction from the heating muffle to the cooling muffle (hereinafter the cross section is called a thermal conducting cross section), heat transfer from the heating muffle to the cooling muffle through the cross section can be effectively suppressed. The wall that has a smaller thickness in part is a wall having a recess (for example, a groove).
(3) At least a part of the thermal insulating structural member is formed of a thin plate. In other words, at least a part of wall of the thermal insulating structural member is made of a thin plate. The xe2x80x9cthin platexe2x80x9d herein refers to a plate-like member that is thinner the cooling muffle wall. This thermal insulating structural member is formed of the plate-like member that has a smaller thermal conducting cross section at least in part, similar to the case of (2), and effectively suppresses thermal conduction between the muffles.
The thermal insulating structural member may be constructed with a combination of at least two of the constitutions (1) through (3). The thermal insulating structural member is preferably constituted so that it reduces the thermal energy supplied to the thermal treatment apparatus by 10% or more compared to the thermal energy supplied to a thermal treatment apparatus without the thermal insulating structural member.
In the thermal treatment apparatus of the present invention, a thermal blocking plate member is preferably disposed at at least one end of the thermal insulating structural member without impeding the passage of the object to be treated.
The thermal blocking plate member is a plate-like member that prevents convective heat transfer which could, occur between spaces separated by the plate-like member if the plate-like member is not provided, and also that provides a surface that prevents heat transfer through thermal radiation from one space to the other.
The thermal blocking plate member preferably has a surface of high thermal reflectivity such as a mirror surface, in order to minimize the heat loss due to radiation of heat from the surface.
The thermal blocking plate member is disposed at at least one end of the thermal insulating structural member. This causes a part of the hollow of the thermal insulating structural member and the thermal treatment zone in the muffle to be separated by the thermal blocking plate member at the end of the thermal insulating structural member. Each end of the thermal insulating structural member may also be regarded as the end of each muffle, which end makes contact with the thermal insulating structural member. Therefore, the embodiment having the thermal blocking plate member disposed at at least one end of the thermal insulating structural member includes an embodiment wherein the thermal blocking plate member is interposed between the thermal insulating structural member and the muffle, wherein the thermal blocking plate member is attached to the inside surface of the muffle wall by, for example, welding or bonding at the end of the muffle. The thermal blocking plate member is disposed so that the surface that prevents heat transfer forms an angle with (namely not in parallel to) the direction of heat transfer (usually the direction of transporting the object to be treated). Preferably, the surface of the thermal blocking plate member which prevents heat transfer crosses the direction of heat transfer at right angles.
Alternatively, the thermal blocking plate member may be provided inside the tunnel, namely the hollow of the thermal insulating structural member. In this case, the thermal blocking plate member is attached to the inside surface of the wall of the thermal insulating structural member by welding or bonding. Or, alternatively, the thermal blocking plate member may also be interposed between two parts which constitute the thermal insulating structural member.
The thermal blocking plate member is provided without impeding the passage of the object to be treated. Specifically, the passage of the object will not be impeded when the thermal blocking plate member is provided with an opening or a notch so that the object and a carrier, as the case may be, pass through the opening or the notch.
Use of the thermal blocking plate member makes it possible to effectively reduce heat transfer through the convection between the atmosphere in the heating muffle and the atmosphere in the cooling muffle, and through the thermal radiation from the inside surface of the heating muffle wall. Thus it is possible to further reduce the heat loss in the thermal treatment apparatus by using combination of the thermal blocking plate member and the thermal insulating structural member.
The thermal insulating structural member to be combined with the thermal blocking plate member is any one of the constitutions (1) through (3) or a combination of at least two of the constitutions (1) through (3).
While the thermal treatment apparatus including muffles as the thermal treatment chambers has been described as the first aspect of the present invention, the present invention can also be applied to a thermal treatment apparatus that has a plurality of thermal treatment chambers that are not muffles. For example, such thermal treatment apparatus has heating means or cooling means provided in the thermal treatment chamber so that the object to be treated is directly heated or cooled.
Thus, according to a second aspect of the present invention, there is provided a thermal treatment apparatus which comprises a plurality of thermal treatment chambers so as to apply a thermal treatment to an object to be treated that is being transported through the thermal treatment chambers, wherein at least one pair of two adjacent thermal treatment chambers of which inside temperatures are different from each other are connected through a thermal insulating structural member-and the thermal insulating structural member has a tunnel structure so as to allow the object to be treated to pass therethrough. The thermal treatment apparatus provided according to the second aspect of the present invention includes the thermal treatment apparatus provided according to the first aspect of the present invention. In other words, the thermal treatment apparatus provided according to the first aspect is a variation of the thermal treatment apparatus provided according to the second aspect wherein at least one pair of the two adjacent thermal treatment chambers of which inside temperatures are different from each other are muffles and the two muffles are connected through the thermal insulating structural member.
In this thermal treatment apparatus, the thermal insulating structural member is inserted between the walls that define the two thermal treatment chambers respectively, so that it effectively suppresses thermal conduction between the thermal treatment chambers. The specific constitution of the thermal insulating structural member is similar to that described previously in conjunction with the thermal insulating structural member disposed between the muffles, and is selected depending on such conditions as the material and thickness of the wall of the thermal treatment chamber.
In the thermal treatment apparatus provided according to the second aspect, as well, the thermal blocking plate member is preferably used in combination with the thermal insulating structural member. Heat loss in the thermal treatment apparatus can also be smaller in this case.
In the thermal treatment apparatus of the present invention described above, the thermal insulating structural member is disposed between the two adjacent thermal treatment chambers (muffles in the case of the muffle furnace) wherein thermal conduction takes place across the joint. Thus the thermal insulating structural member is disposed between a high temperature thermal treatment chamber and a low temperature thermal treatment chamber (between a high temperature muffle and a low temperature muffle in the case of the muffle furnace), wherein the inside temperature (generally the temperature of the atmosphere gas in the thermal treatment chamber) of one of the thermal treatment chambers is higher than that of the other.
The larger the temperature difference between the thermal treatment chambers, the larger the heat loss caused by thermal conduction, which is desired to be reduced. Therefore, when the temperature difference between the two adjacent thermal treatment chambers is larger, it is more desirable to provide the thermal insulating structural member between the thermal treatment chambers, thus achieving greater effect of decreasing the heat loss. A preferable combination of the thermal treatment chambers between which the thermal insulating structural member is disposed is, for example, a combination wherein one thermal treatment chamber is a heating chamber or a slow cooling chamber of which an inside of is heated by a heater or the like to 400xc2x0 C. or higher, and the other thermal treatment chamber is a cooling chamber (quenching chamber) that is cooled by means of a cooling medium such as water so that the inside temperature thereof is around room temperature.
Even when both of the two adjacent thermal treatment chambers are heated by a heater or the like, a temperature in one of the thermal treatment chambers may be set to be higher than that of the other by several tens of degrees Celsius (for example 20xc2x0 C.). As such a combination of the two adjacent thermal treatment chambers, there is a combination of a heating chamber that is heated to a lower temperature and a heating chamber that is heated to a higher temperature. The thermal insulating structural member may be disposed between such two thermal treatment chambers that adjoin each other.
When the thermal blocking plate member is used, the thermal blocking plate member is preferably disposed at the end of the thermal insulating structural member which makes contact with the thermal treatment chamber having a higher inside temperature (heating chamber). Heat loss can be made smaller by providing the thermal blocking plate member near the thermal treatment chamber of higher temperature.
The effects that can be achieved by the thermal treatment apparatus of the present invention are as follows. The thermal treatment apparatus of the present invention is characterized by the thermal insulating structural member disposed between the two adjacent thermal treatment chambers (for example, muffles) and, as the case may be, the thermal blocking plate member disposed therein. As this constitution reduces the heat loss in the thermal treatment apparatus (for example, muffle structure heating furnace), total thermal energy consumed in the thermal treatment apparatus can be reduced. According to the present invention, therefore, energy saving in the operation can be achieved and the products can be manufactured with lower running cost without adversely affecting the quality and yield of the products subjected to the thermal treatment.
The thermal insulating structural member and the thermal blocking plate member do not include any member that is moved (for example, up and down) mechanically by means of a motor or the like. As a result, the thermal treatment apparatus of the present invention achieves the effects described above satisfactorily even when the temperature in one of the two adjacent thermal treatment chambers is so high as to make it difficult for the motor or the like to make mechanical movement.
Moreover, the thermal insulating structural member and the thermal blocking plate member can suppress the thermal conduction between the two adjacent thermal treatment chambers without allowing the atmosphere gas in the thermal treatment chambers to leak to the outside of the thermal treatment chambers. Therefore, the thermal treatment apparatus of the present invention can stably apply a thermal treatment to the object to be treated with a higher effective heat efficiency without disturbing the atmosphere gas in the thermal treatment chambers.